Hydraulically operated clutches are used for shifting gears in modern automatic transmissions of automobiles. To enable these switching operations to take place smoothly and without being noticeable to the driver, it is necessary to set the hydraulic pressure at the clutches with maximum precision according to predefined pressure ramps. Electromagnetically operated pressure control valves are used for this purpose. These valves may be designed either as seat valves or slide valves. As a rule, both structural designs have three hydraulic ports for inflow, control pressure and return flow. In seat valves, the ports may usually be situated both axially and radially.
A seat valve of this type is described in German Patent Application No. DE 197 33 660. The exemplary embodiments illustrated therein have both radial and axial inflow ports.
To maintain the pressure control function of slide valves, it is necessary for either tank pressure or control pressure to be present at the end faces of the slide or control piston. Therefore, the corresponding ports are usually situated radially. A slide valve of this type is described in German Patent Application No. DE 201 00 950 U1, it being possible to connect the tank port axially in one exemplary embodiment. A slide valve having an axially situated working port, at which the desired control pressure is present, is described in German Patent Application No. DE 198 47 021 B4.
Modern transmission control systems have hydraulic lines of high complexity. Due to the limited installation space, it is often not possible to separate the supply lines in a way that enables these lines to be routed to the pressure control valves in any manner.